The subject matter disclosed herein relates to diagnosing in-line critical dimension control adjustments. More specifically, the subject matter disclosed herein relates to using optical proximity correction verification (OPCV) to account for in-line critical dimension control adjustments.
OPCV simulations are most accurate when lithographic in-line conditions are run at the same conditions as used during the processing of wafers for model building. However, it is common in conventional approaches for the line to control the lithography conditions such that a specific structure (e.g., a control structure) is printed at a target critical dimension (CD). In these cases, it is not unusual for the conditions of the line to differ from the conditions of the OPCV simulations, for example, because of process drifts over time, because the initial model was not properly anchored to the structure used to control the manufacturing line, or because there is a desire for the target of the process to be increased or decreased for electrical or yield performance reasons. For example, the in-line target CD (and thus, the exposure dose used) may drift over time due to, e.g., feedback from the test structure. Therefore, the pass/fail criteria may not accurately predict fails in-line.
Two conventional approaches to addressing this issue exist. The first approach involves ignoring the dose differences between the in-line target CD and the OPCV simulations. This approach, however, may create inaccuracies in prediction of the lithography. The second approach involves continually updating the production code to reflect changes in the in-line dose from the time the model was built through the time of OPCV simulation. However, this approach can introduce error in the lithography, because the dose setting used may not reflect the true dose applied, due to issues such as dose calibration, reflectivity, thin film interference, etc.